1. Field of the Invention
The present invention relates to the development and use of pyrolytic products or chars made from poultry manure that possess excellent adsorption properties, particularly with respect to the uptake of metal ions.
2. Description of the Prior Art
Pyrolytic products or chars are low porosity, low surface area materials that are intermediate products in the development of activated carbons. They are generally not used in industry for purification and chemical recovery operations as well as environmental remediation, as are the more structurally developed activated carbons. Toxic metals contamination of various water sources is a significant problem in many parts of the United States. Chars, which can be produced from a number of precursor materials including coal, wood and agricultural plant wastes, have not been examined for remediation of this problem. There are few if any commercial outlets for chars because of their inferior adsorption characteristics compared to activated carbon. While carbon production is an expanding industry in the United States, with a present production rate of over 400 million pounds a year and a growth rate of over 3% annually, char production is simply an intermediate step in carbon manufacture and has no significant presence in the marketplace.
The production of pyrolytic products, in the form of chars, is an age-old art. Char, when produced in the absence of air by non-oxidative carbonization or pyrolysis, is a relatively inactive material possessing a surface area limited to several square meters per gram. Chars are normally produced to reduce the volume and mass of a particular feedstock and provide a soil amender that improves the physical and nutritive properties through its ash content of hard, compact soils with a high clay content or highly porous soils with a high silica or sand content. Because chars have poorly developed internal structure, they adsorb few if any metal ions or organic compounds and non-polar materials from either liquid or gaseous media.
Chars, because of their association with activated carbon, traditionally have been made by pyrolysis of plant feedstock, from decomposed plant material such as coal to fresh plant material such as coconut shells and wood. Plant feedstock has a relatively high elemental carbon content, especially decomposed plant material, and elemental carbon yields derived from plant feedstock are considered acceptable in the carbon industry. Very few studies have evaluated animal waste as source of pyrolytic products. Animal waste generally has lower elemental carbon content and may produce lower char yields than plant material when both sources are pyrolyzed under the same time and temperature conditions. Chars derived from plant, animal, and human by-products have recently been shown to be porous materials that possess some useful nitrogen compounds and minerals such as calcium, magnesium, potassium, and phosphorus. Harmful substances, such as arsenic and metals such as mercury, lead, and cadmium, were shown to be present in very small concentrations.
Shinogi et al., in their paper entitled “Basic Characteristics of Low-Temperature Carbon Products from Waste Sludge” (Adv. Environ. Res., 2003, 7, 661-665) prepared a pyrolysis product of cattle manure by heating to 380° C. in an atmosphere of limited air and reported the properties of the product. The pyrolysis product had a very low surface area of 2.2 m2/g, an ash content of 25.6% and an elemental carbon content of 49.2%. The authors described the main use for the pyrolysis product as a soil amender due to the high phosphate ion, organic nitrate, and potassium ion content. In a second paper entitled “Pyrolysis of Plant, Animal and Human Waste: Physical and Chemical Characterization of the Pyrolytic Products” (Biosresource Technol. 2003, 90, 241-247), Shinogi et al. also described the production of pyrolyzed cattle manure over the temperature range of 250-800° C. in closed containers. Surface areas were low (<20 m2/g) over this temperature range. The pyrolyzed cattle manure also had high ash content (up to 60%), a high pH (>10) and a total carbon content of less than 40%.
Bilitewski, in a paper entitled “Production and Possible Applications of Activated Carbon from Waste” (Recycling Berlin, '79 Int. Recycling Cong. Thome-Kozimiensky, Ed, Berlin V1, 1979, 714-721) produced carbon from poultry droppings by steam activation in a fluidized bed reactor. He reported that poultry droppings produced a carbon with a surface area of 60.5 m2/g, elemental carbon content of 27.5% and an ash content of 52.4%. The author concluded that poultry droppings will yield only a very low grade carbon mainly due to its low surface area and high ash content.
Chen et al., in an article entitled “Physical and Chemical Properties Study of the Activated Carbon made from Sewage Sludge” (Waste Management, 2002, 22,755-760) used zinc chloride to chemically activate sewage sludge and evaluated select physical and chemical properties of the resultant activated carbon. The carbon had a surface area of 647 m2/g and was 38.9% elemental carbon. Additionally, the carbon had 5.18 meq/g oxygen-containing surface functional groups and possessed adsorption toward phenol and carbon tetrachloride.
Martin et al., in a publication entitled “Feasibility of Activated Carbon Production from Biological Sludge by Chemical Activation with ZnCl2 and H2SO4” (Environ. Technol., 1996, 17, 667-672) employed either zinc chloride or sulfuric acid to produce activated carbons from surplus biological sludge obtained from a wastewater treatment plant. Under optimal activation conditions, which was achieved with sulfuric acid, the activated carbon had a surface area of 257 m2/g, an ash content of 38% and a yield of 34%. Removal of phenol using the optimally produced carbon was determined and found to be about 20% of the phenol removal capability of a commercial activated carbon.
Tay et al., in a publication entitled “A Comparative Study of Anaerobically Digested and Undigested Sewage Sludges in Preparation of Activated Carbons” (Chemosphere, 2001, 44, 53-57) reported on the zinc chloride activation of both digested and undigested sewage sludges. The results indicated that the undigested sludge had a higher carbon content and lower ash content and, accordingly, yielded a better activated carbon with a higher surface area, pore volume, carbon content and phenol adsorption capacity than its digested counterpart.
While various methodologies exist for the creation of activated carbons from plant or plant-derived material that are effective in the adsorption of metal ions, there remains a need to create lower cost pyrolytic products, such as chars, from alternate sources of carbonaceous material that are in great abundance and that have enhanced adsorption properties toward metal ions. We describe a method and product that provides chars from poultry manure with excellent metal ion adsorptive properties.